PHOTO: An asteroid impact caused the last mass extinction event, which occurred 65 million years ago. (NASA: Reuters)
Humans could wipe out three quarters of the Earth’s species within 240 to 500 years in an event known as a mass extinction, a Hobart-based scientist says.
A mass extinction occurs when Earth loses more than 75 per cent of its species in a geologically short time frame.
There have been five mass extinctions – known as the “Big Five” – in the past 540 million years. Those events were caused by asteroid collisions, climate fluctuations and volcanic eruptions.
For the first time, however, a species could be the cause of a mass extinction event.
Professor Mike Coffin, a marine geophysicist from the University of Tasmania, told a conference in Hobart on Saturday that humans are on track to bring about the demise of 75 per cent of the Earth’s species within a frighteningly short time period.
The ‘Big Five’ mass extinctions
The Ordovician event, about 443 million years ago. An estimated 86 per cent of species were lost due to the onset of glacial and interglacial episodes, changing atmospheric and ocean chemistry, and the sequestration of carbon dioxide.
The Devonian event, about 359 million years ago. An estimated 75 per cent of species were lost as a result of global cooling, followed by global warming. There is debate over the timing and importance of asteroid impacts.
The Permian event, about 251 million years ago. An estimated 96 per cent of species were lost after a massive volcanic eruption in the Siberian Traps, global warming, and deep marine anoxic waters. There is debate over the evidence of an asteroid impact.
The Triassic event, about 200 million years ago. An estimated 80 per cent of life was lost after volcanic activity lifted the amount of carbon dioxide in the atmosphere.
The Cretaceous event, about 65 million years ago. An asteroid impact is thought to have led to “global cataclysm”.
Source: Has the Earth’s sixth mass extinction already arrived? (Barnosky et al. 2011) Published in the journal Nature.
He said current figures show that Earth’s species are declining at a rate that could see mass extinction levels reached in just 240 years.
“We’re on a trajectory to reach the 75 per cent level some time between 240 and 2,000 years from now,” he said.
“Based on all threatened species as defined by the International Union for the Conservation of Nature … assuming all of those threatened species become extinct then we would reach mass extinction somewhere between 240 and 540 years from now.”
Professor Coffin said the best estimates are that about 8.7 million species are currently alive on Earth, although scientists cannot know for sure.
Those numbers include viruses and bacteria, and Professor Coffin said scientists are yet to discover the vast majority of species.
“I think of that 8.7 million we think there are now, we’ve only [discovered] about 15 per cent,” he told ABC News Online.
“So there is still 85 per cent that are yet to be discovered and or described.”
Humans ‘good at driving mass extinction’
Researchers say humans are causing the extinction of species in a number of ways, from changing the global climate to killing species directly.
The last mass extinction occurred 65 million years ago when an asteroid slammed into the Earth, triggering the demise of the dinosaurs.
“Homosapians have been around for 200,000 years – that’s the length of our reign. The dinosaurs were around for 165 millions years, so we’re just a little blip on the geological time-scale,” Professor Coffin said.
“We haven’t been around very long but we seem to be very good a driving a mass extinction ourselves.”
And in the case of a mass extinction arising from an asteroid impact, what would be most likely to survive?
Species like us that don’t reproduce until we’re in our teens at earliest, with long gestation periods and that take a long time to evolve or adapt – big mammals – we’re most vulnerable.
Professor Mike Coffin
Professor Coffin said small animals that can breed quickly and adapt, such as cockroaches, would be well equipped.
As mammals, Professor Coffin said humans would face difficulties.
“Species like us that don’t reproduce until we’re in our teens at earliest, with long gestation periods and that take a long time to evolve or adapt – big mammals – we’re most vulnerable,” he said.
But he said ultimately it is very unlikely that humans will destroy all of Earth’s life forms.
“I don’t think humans will drive life completely off the planet,” he said.
“Prior to the explosion of multi-cellular life 540 million years ago there were at least two episodes where the total surface of the Earth froze over – we call that a Snowball Earth.
“There was single cell life back then, and even though the entire planet froze over some of that life survived. That’s why we are here today.”
Professor Coffin says he hopes awareness of the potential mass extinction will push communities and governments to take action to stem the decline in the number of species.